1. Field of the Invention
The present invention relates to an umbilical-member managing system for an industrial robot. The present invention may be applied, for example, to a system for laying and managing a torch cable in an arc welding robot.
2. Description of the Related Art
Typically, an industrial robot is used in a condition where a working tool (i.e., an end effector) is attached to the distal end of a wrist. Electrical energy, an electric signal and/or a substance such as a gas or a liquid are supplied to the working tool through a cable, a pipe, etc. For example, in a welding robot with a welding torch mounted thereon as a working tool, a welding wire is supplied to the welding torch through a torch cable. In the present application, a member such as a cable, a pipe, etc., used for supplying energy, a signal, a substance (including a welding wire), or the like, to a working tool, is generally referred to as an “umbilical member”.
At a site where an industrial robot (hereinafter simply referred to as a “robot”) is used, various objects such as a workpiece, a jig, peripheral equipment, etc., are present around the robot, so that the robot often has to be operated to insert the working tool into a narrow space between such various objects. In this case, the arm, the wrist and the working tool, provided at the distal end of the robot, can operate in a relatively narrow space, which substantially eliminates a problem of interference between them and surrounding objects. However, it is very difficult to lay and manage the above-described umbilical member for the working tool without giving rise to interference with the surrounding objects. From a requirement for ensuring a minimum radius of curvature, the umbilical member is usually laid in a gently curved form, and as a result, the operational space of the robot is enlarged, which leads to a problem of interference with the surrounding objects. In other words, in the conventional configuration, the umbilical member is liable to interfere with objects such as a workpiece, a jig or peripheral equipment.
Conventionally, several techniques have been proposed in order to overcome the problem of interference of an umbilical member with surrounding objects. For example, Japanese Unexamined Utility Model Publication (Kokai) No. 5-28563 (JP 5-28563 U) discloses an arc welding robot requiring a welding wire to be supplied to a welding torch, in which a wire feeding device is mounted on a support base provided in a robot arm. FIGS. 1A and 1B schematically show the configuration of this arc welding robot, in which FIG. 1A is a front view showing the entire configuration of the welding robot, and FIG. 1B is a side view showing the distal end region of the arm of the welding robot as seen from the left side of FIG. 1.
As shown in FIG. 1A, in this arc welding robot, a welding torch 2 is attached to the distal end of a wrist of a robot mechanical section 1, and a wire feeding device 4 is mounted on a support base 5 of a robot arm (forearm) for feeding a welding wire to the welding torch 2 through a torch cable 3. The wire feeding device 4 is constructed so as to be adjustable in reciprocating motion (or slidable) along the feeding direction of the welding wire, through a shift unit (or a slide mechanism) 6 adapted to be controlled for the position thereof by a control section (not shown) for the robot arm. Thus, even when the wrist or the arm moves to some extent, the wire feeding device 4 is displaced and, thereby, the tension applied to the torch cable is reduced.
However, when a wrist axis provided in the robot performs an orientation change (i.e., a turning) of the welding torch 2, the behavior of the torch cable 3 exhibits a large change, as shown by broken lines 3a, 3b in FIG. 1B, due to the turning motion of the welding torch 2 (see broken lines 2a, 2b), which increases the possibility of interference between the torch cable 3 and surrounding objects. The torch cable 3 may also be excessively pulled and thus be entangled with the forearm, or the torch cable 3 may be excessively loosened and thus be significantly changed in curvature thereof (i.e., radius of curvature). This arises because the turning axis of the wrist is located to intersect with the distal end of the forearm, and because the torch cable 3 is supported by a support stay 7 extending from the support base 5 at a position above the turning axis of the wrist.
As an alternative technology, Japanese Unexamined Patent Publication (Kokai) No. 2001-179443 (JP 2001-179443 A) discloses a support structure for a wire feeding device used for feeding a welding wire to a welding torch in a welding robot, wherein the wire feeding device is slidably supported on a support unit provided on the ceiling, etc., of a building so as to be permitted to follow the movement of the welding torch. Also, Japanese Unexamined Patent Publication (Kokai) No. 2002-166386 (JP 2002-166386 A) discloses a guide unit for guiding a cable laid between several components of a robot, in which a guide rail in the shape of a circular arc is provided on the forearm of the robot, and a cable holder is attached rotatably to a runner movable along the guide rail.
As shown by way of example in FIGS. 1A and 1B, when the orientation of a working tool, such as a welding torch, attached to a distal end of a robot's wrist is to be changed, the working tool is usually turned relative to a robot arm (i.e., a manipulator). As a result, when the orientation of the working tool is changed during the operation thereof, an umbilical member, such as a cable or a pipe, for the working tool may be excessively pulled, or may be excessively loosened to significantly change the curvature thereof. Under the excessive pulling, the umbilical member may be entangled with the forearm. Alternatively, due to the excessive loosening, the umbilical member may interfere with surrounding equipment. Further, it is difficult in practice to simulate such a complicated behavior of the umbilical member, which prevents an operating program of the robot operation from being prepared in an off-line process.